Heat exchanger capacity for one or more heat exchangers associated with a power gearbox of a turbofan engine

ABSTRACT

A turbofan engine having one or more heat exchangers tied to a power gearbox is provided. The power gearbox mechanically couples a low pressure spool and a fan of the turbofan engine. The one or more heat exchangers have a heat exchanger capacity defined by a resultant heat transfer surface area density associated with the one or more heat exchangers multiplied by a heat conductance factor that relates a power gearbox heat load, a fan power consumption function, a fan diameter of the fan, and a bypass ratio of the turbofan engine. The heat exchanger capacity is between 0.77 and 48 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m2/m3 and 13,000 m2/m3.

FIELD

The present disclosure relates to heat exchangers associated with a power gearbox of a turbofan engine.

BACKGROUND

A turbofan engine can include a power gearbox that acts as a speed reducer between a low pressure spool and a fan thereof. The power gearbox may also be called a main gearbox. The power gearbox can generate significant heat during operation.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present disclosure, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 provides a schematic cross-sectional view of a turbofan engine in accordance with an example embodiment of the present disclosure;

FIG. 2 provides a perspective view of a heat exchanger of the turbofan engine of FIG. 1 ;

FIG. 3 provides a perspective view of an exchanger unit of the heat exchanger of FIG. 2 ;

FIG. 4 provides a cross-sectional view of a core of the exchanger unit taken along line 4-4 of FIG. 3 ;

FIG. 5 lists various relationships between heat exchanger characteristics and operational and architectural characteristics of a turbofan engine in accordance with example embodiments of the present disclosure;

FIGS. 6 through 12 each graphically depict a heat exchanger capacity of one or more heat exchangers tied to a power gearbox of a turbofan engine as a function of a rotational speed of a low pressure spool of the turbofan engine in accordance with example embodiments of the present disclosure;

FIG. 13 provides a table listing values for different example turbofan engines in accordance with example embodiments of the present disclosure; and

FIG. 14 provides a flow diagram for a method of operating a turbofan engine having one or more heat exchangers tied to a power gearbox mechanically coupling a spool and a fan in accordance with an example embodiment of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to present embodiments of the disclosure, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the disclosure.

As used herein, the terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components.

The terms “coupled,” “fixed,” “attached to,” and the like refer to both direct coupling, fixing, or attaching, as well as indirect coupling, fixing, or attaching through one or more intermediate components or features, unless otherwise specified herein.

The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.

The term “at least one of” in the context of, e.g., “at least one of A, B, and C” refers only A, only B, only C, or any combination of A, B, and C.

Here and throughout the specification and claims, range limitations are combined and interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. For example, all ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other.

As used herein, a heat exchanger is considered “tied” to a power gearbox where the heat exchanger is configured to process at least a portion of the heat load of the power gearbox.

A turbofan engine can include a power gearbox that mechanically couples a low pressure spool and a fan of the turbofan engine. The power gearbox may act as a speed reducer between the low pressure spool and the fan. During operation, the power gearbox can generate significant heat. Accordingly, such a geared turbofan engine can include one or more heat exchangers for processing the heat load generated by the power gearbox. Designing a gas turbine engine having one or more heat exchangers tied to the power gearbox can present certain challenges. For instance, there are certain challenges with designing a gas turbine engine having one or more heat exchangers, which are tied to the power gearbox, that are both compact and able to effectively process heat duty of the power gearbox.

The inventors of the present disclosure have developed architectures for a turbofan engine having one or more heat exchangers tied to a power gearbox, wherein the one or more heat exchangers are both compact and able to effectively process heat duty. Particularly, the inventors proceeded in the manner of designing a turbofan engine with given fan, bypass ratio, and power gearbox characteristics as well as characteristics of one or more heat exchangers tied to a power gearbox of the turbofan engine; checking the compactness and efficiency of the one or more heat exchangers given the characteristics of the fan, bypass ratio, and power gearbox characteristics as well as characteristics of the one or more heat exchangers; redesigning the turbofan engine, power gearbox, and/or one or more heat exchangers when changes were made to, e.g., the fan diameter, gear ratio of the power gearbox, packaging requirements/mounting affecting heat exchanger design constraints, bypass ratio characteristics, and the area and/or volume of the channels of the one or more heat exchangers; rechecking the compactness and efficiency of the one or more heat exchangers given the characteristics of the fan, bypass ratio, and power gearbox characteristics as well as characteristics of the one or more heat exchangers; etc. during the design of several different types of gas turbine engines, including the turbofan engine described below with reference to FIG. 1 .

During the course of this practice of studying/evaluating various fan architectures, gear ratios for the power gearbox, bypass ratios, and heat exchanger characteristics considered feasible for best satisfying mission requirements, a relationship was unexpectedly discovered between the compactness of the one or more heat exchangers and the ease of heat load distribution to the one or more heat exchangers. This relationship is represented by a heat exchanger capacity. The heat exchanger capacity can be thought of as an indicator of the compactness and effectiveness of one or more heat exchangers tied to a power gearbox to process the heat duty of the power gearbox given the architectural arrangement of the turbofan engine and the power gearbox. The inventors have found that a turbofan engine having one or more heat exchangers, which are tied to a power gearbox, that have a heat exchanger capacity within a range specified herein renders one or more heat exchangers that are both optimally compact and effective at processing heat duty associated with the power gearbox.

Referring now to the drawings, FIG. 1 provides a schematic cross-sectional view of a turbofan engine 100 according to an example embodiment of the present disclosure. For the depicted embodiment of FIG. 1 , the turbofan engine 100 is an aeronautical, high-bypass turbofan engine configured to be mounted to an aircraft, e.g., in an under-wing configuration. As shown, the turbofan engine 100 defines an axial direction A, a radial direction R, and a circumferential direction C. The axial direction A extends parallel to or coaxial with a longitudinal centerline 102 defined by the turbofan engine 100.

The turbofan engine 100 includes a fan section 104 and an engine core 106 disposed downstream of the fan section 104. The engine core 106 includes an engine cowl 108 that defines an annular core inlet 110. The engine cowl 108 encases, in a serial flow relationship, a compressor section 112 including a first, booster or LP compressor 114 and a second, HP compressor 116; a combustion section 118; a turbine section 120 including a first, HP turbine 122 and a second, LP turbine 124; and an exhaust section 126. The compressor section 112, combustion section 118, turbine section 120, and exhaust section 126 together define a core air flowpath 132 through the engine core 106.

An HP shaft 128 drivingly connects the HP turbine 122 to the HP compressor 116. An LP shaft 130 drivingly connects the LP turbine 124 to the LP compressor 114. The HP shaft 128, the rotating components of the HP compressor 116 that are mechanically coupled with the HP shaft 128, and the rotating components of the HP turbine 122 that are mechanically coupled with the HP shaft 128 collectively form a high pressure spool 131, or HP spool. The LP shaft 130, the rotating components of the LP compressor 114 that are mechanically coupled with the LP shaft 130, and the rotating components of the LP turbine 124 that are mechanically coupled with the LP shaft 130 collectively form a low pressure spool 133, or LP spool.

The fan section 104 includes a fan assembly 138 having a fan 134 mechanically coupled with a fan rotor 140. The fan 134 has a plurality of fan blades 136 circumferentially-spaced apart from one another. As depicted, the fan blades 136 extend outward from the fan rotor 140 generally along the radial direction R. A power gearbox 142 mechanically couples the LP spool 133 and the fan rotor 140. The power gearbox 142 may also be called a main gearbox. The power gearbox 142 includes a plurality of gears for stepping down the rotational speed of the LP shaft 130 to provide a more efficient rotational fan speed of the fan 134. In other example embodiments, the fan blades 136 of the fan 134 can be mechanically coupled with a suitable actuation member configured to pitch the fan blades 136 about respective pitch axes, e.g., in unison.

Referring still to FIG. 1 , the fan rotor 140 and hubs of the fan blades 136 are covered by a rotatable spinner 144 aerodynamically contoured to promote an airflow through the plurality of fan blades 136. Additionally, the fan section 104 includes an annular fan casing or outer nacelle 146 that circumferentially surrounds the fan 134 and/or at least a portion of the engine core 106. The nacelle 146 is supported relative to the engine core 106 by a plurality of circumferentially-spaced outlet guide vanes 148. A downstream section 150 of the nacelle 146 extends over an outer portion of the engine core 106 so as to define a bypass passage 152 therebetween.

During operation of the turbofan engine 100, a volume of air 154 enters the turbofan engine 100 through an associated inlet 156 of the nacelle 146 and/or fan section 104. As the volume of air 154 passes across the fan blades 136, a first portion of air 158 is directed or routed into the bypass passage 152 and a second portion of air 160 is directed or routed into the core inlet 110. The pressure of the second portion of air 160 is progressively increased as it flows downstream through the LP compressor 114 and HP compressor 116. Particularly, the LP compressor 114 includes sequential stages of LP compressor stator vanes 182 and LP compressor blades 184 that progressively compress the second portion of air 160. The LP compressor blades 184 are mechanically coupled to the LP shaft 130. Similarly, the HP compressor 116 includes sequential stages of HP compressor stator vanes 186 and HP compressor blades 188 that progressively compress the second portion of air 160 even further. The HP compressor blades 188 are mechanically coupled to the HP shaft 128. The compressed second portion of air 160 is then discharged from the compressor section 112 into the combustion section 118.

The compressed second portion of air 160 discharged from the compressor section 112 mixes with fuel and is burned within a combustor of the combustion section 118 to provide combustion gases 162. The combustion gases 162 are routed from the combustion section 118 along a hot gas path 174 of the core air flowpath 132 through the HP turbine 122 where a portion of thermal and/or kinetic energy from the combustion gases 162 is extracted via sequential stages of HP turbine stator vanes 164 and HP turbine blades 166. The HP turbine blades 166 are mechanically coupled to the HP shaft 128. Thus, when the HP turbine blades 166 extract energy from the combustion gases 162, the HP shaft 128 rotates, thereby supporting operation of the HP compressor 116. The combustion gases 162 are routed through the LP turbine 124 where a second portion of thermal and kinetic energy is extracted from the combustion gases 162 via sequential stages of LP turbine stator vanes 168 and LP turbine blades 170. The LP turbine blades 170 are coupled to the LP shaft 130. Thus, when the LP turbine blades 170 extract energy from the combustion gases 162, the LP shaft 130 rotates, thereby supporting operation of the LP compressor 114, as well as the fan 134 by way of the power gearbox 142.

The combustion gases 162 are subsequently routed through the exhaust section 126 of the engine core 106 to provide propulsive thrust. Simultaneously, the pressure of the first portion of air 158 is substantially increased as the first portion of air 158 is routed through the bypass passage 152 before it is exhausted from a fan nozzle exhaust section 172 of the turbofan engine 100, also providing propulsive thrust. The HP turbine 122, the LP turbine 124, and the exhaust section 126 at least partially define the hot gas path 174 for routing the combustion gases 162 through the engine core 106.

As further shown in FIG. 1 , the turbofan engine 100 includes a cooling system 190 for cooling various components, such as the power gearbox 142. The cooling system 190 includes one or more heat exchangers 192. For this embodiment, the one or more heat exchangers 192 include four (4) heat exchangers, including a first heat exchanger 192A, a second heat exchanger 192B, a third heat exchanger 192C, and a fourth heat exchanger 192D. The heat exchangers 192 can each be any suitable type of heat exchanger, such as, without limitation, a fuel-to-oil heat exchanger, an air-to-oil heat exchanger, or an oil-to-oil heat exchanger. In this regard, the one or more heat exchangers 192 can include one or more of a fuel-to-oil heat exchanger, an air-to-oil heat exchanger, an oil-to-oil heat exchanger, some combination thereof, etc.

The one or more heat exchangers 192 are configured to receive one or more first fluids F1 from the power gearbox 142, e.g., via one or more fluid supply conduits 194 (only one shown in FIG. 1 ). The one or more first fluids F1 received from the power gearbox 142 can be, for example, oil, one or more other transmission fluids, one or more lubrication fluids, some combination thereof, etc. For instance, the power gearbox 142 can include an oil pump configured to pump oil through the power gearbox 142, as well as from the power gearbox 142 to the one or more heat exchangers 192 and back to the power gearbox 142, e.g., via one or more fluid return conduits 195 (only one shown in FIG. 1 ). In this regard, the oil pump of the power gearbox 142 can circulate oil between the power gearbox 142 and the one or more heat exchangers 192.

The one or more heat exchangers 192 are also configured to receive one or more second fluids F2 from other sources of the turbofan engine 100 or aircraft to which the turbofan engine 100 is mounted. For instance, the one or more second fluids F2 can include fuel received from a fuel tank, cooled oil received from a scavenge oil tank, air bled from the bypass passage 152 and/or the core air flowpath 132, etc. The one or more second fluids F2 can be used by the one or more heat exchangers 192 to cool the one or more first fluids F1. After exchanging heat with the one or more second fluids F2, the cooled one or more first fluids F1 can be recirculated back to the power gearbox 142, e.g., by the oil pump of the power gearbox 142 via the one or more fluid return conduits 195.

It will be appreciated that the turbofan engine 100 depicted in FIG. 1 is provided by way of example only, and that in other example embodiments, the turbofan engine 100 may have any other suitable configuration. Additionally, or alternatively, aspects of the present disclosure may be utilized with other suitable aeronautical turbofan engine, such as a turboshaft engine, turboprop engine, turbojet engine, etc.

FIG. 2 provides a perspective view of one of the one or more heat exchangers of the turbofan engine 100 of FIG. 1 . Particularly, the first heat exchanger 192A is depicted. The second heat exchanger 192B, the third heat exchanger 192C, and the fourth heat exchanger 192D of FIG. 1 may be configured in a same or similar manner as the first heat exchanger 192A. For instance, the heat exchangers 192B, 192C, 192D may each include a plurality of exchanger units each having a core defining first and second channels, as provided below.

As depicted in FIG. 2 , the first heat exchanger 192A defines a vertical direction V, a lateral direction L, and a transverse direction T that are orthogonal to one another. The first heat exchanger 192A includes a plurality of exchanger units 210. The exchanger units 210 can be compactly arranged in any suitable configuration. For this embodiment, the first heat exchanger 192A includes twenty (20) exchanger units 210, including ten right-side exchanger units 211-220 stacked on top of one another along the vertical direction V and ten left-side exchanger units 221-230 stacked on top of one another along the vertical direction V. Although the first heat exchanger 192A of FIG. 2 has twenty exchanger units 210, in other example embodiments, the first heat exchanger 192A can include any suitable number of exchanger units, such as one exchanger unit, eight exchanger units, fifty exchanger units, etc. Further, in other embodiments, the exchanger units 210 can be positioned side-by-side rather than stacked on one another.

With reference now to FIGS. 2, 3, 4 , FIG. 3 provides a perspective view of a first exchanger unit 211 of the first heat exchanger 192A of FIG. 2 . FIG. 4 provides a cross-sectional view of a core of the first exchanger unit 211 taken along line 4-4 of FIG. 3 . Generally, each exchanger unit 210 of the first heat exchanger 192A has a core and two manifolds. The core of each exchanger unit defines first channels and second channels. The first channels can receive a first fluid and the second channels can receive a second fluid. The core of one or more of the exchanger units 210 can be formed by a plurality of unit cells arranged in flow communication with one another. Alternatively, the core of one or more of the exchanger units 210 can be formed as monolithic blocks.

By way of example, as depicted, the first exchanger unit 211 includes a core 240 defining first channels 241 (outlined by dashed lines in FIG. 4 ) and second channels 242 (outlined by solid lines in FIG. 4 ). The first channels 241 can receive a first fluid F1 and the second channels 242 can receive a second fluid F2. The first fluid F1 and the second fluid F2 can both be any suitable fluid. The first fluid F1 flowing through the first channels 241 can be warmer than the second fluid F2 flowing through the second channels 242. In this way, thermal energy can be exchanged between the first and second fluids F1, F2 as they flow through the first exchanger unit 211. For this embodiment, the first fluid F1 flowing through the first channels 241 (out of the page as represented by the “circled dot” in FIG. 4 ) is in crossflow direction with respect to the second fluid F2 flowing through the second channels 242 (into the page as represented by the “circled X” in FIG. 4 ).

Although the core 240 of the first exchanger unit 211 is shown in a straight channel configuration in FIG. 3 , the core 240 of the first exchanger unit 211 (as well as the cores of the other exchanger units 210) can have other suitable configurations, such as a double U-bend channel configuration, a single U-bend configuration, etc.

The first exchanger unit 211 includes a first manifold 244 and a second manifold 246. Generally, the first manifold 244 distributes the second fluid F2 to the second channels 242 and receives the first fluid F1 from the first channels 241. The first manifold 244 can be arranged to keep the first fluid F1 and the second fluid F2 fluidly separate. Similarly, the second manifold 246 distributes the first fluid F1 to the first channels 241 and receives the second fluid F2 from the second channels 242. The second manifold 246 can be arranged to keep the first fluid F1 and the second fluid F2 fluidly separate. The first manifold 244 and/or second manifold 246 can be in flow communication with a manifold of an adjacent exchanger unit such that the first and/or second fluids F1, F2 can flow between exchanger units 210 of the first heat exchanger 192A.

Each exchanger unit 210 of the first heat exchanger 192A can be configured in a same or similar manner as the first exchanger unit 211 provided above. In this way, each exchanger unit 210 of the first heat exchanger 192A can have a core arranged in a same or similar manner as the core 240 of the first exchanger unit 211 and two manifolds arranged in a same or similar manner as the first and second manifolds 244, 246 of the first exchanger unit 211. The core of each exchanger unit 210 defines first channels and second channels just as the core 240 defines the defines the first channels 241 and the second channels 242.

As alluded to earlier, the inventors discovered, unexpectedly during the course of engine design, that a relationship exists between the compactness of one or more heat exchangers tied to a power gearbox of a turbofan engine and the heat load distribution to the one or more heat exchangers. This relationship is represented by a heat exchanger capacity. The inventors found that one or more heat exchangers having a heat exchanger capacity within one of the ranges specified below provides one or more heat exchangers that are both optimally compact and effective at processing the heat duty associated with a power gearbox of a turbofan engine.

The heat exchanger capacity is a dimensionless quantity that relates a heat transfer surface area density associated with the one or more heat exchangers and a heat conductance factor that relates certain operational and architectural characteristics of the power gearbox and the turbofan engine. Particularly, the heat exchanger capacity captures the relationship between a resultant heat transfer surface density of the one or more heat exchangers tied to the power gearbox and a heat conductance factor that relates a power gearbox heat load associated with the power gearbox, a fan power consumption function associated with the fan, a fan diameter of the fan, and a bypass ratio of the turbofan engine. Consequently, the heat exchanger capacity is a function of a resultant heat transfer surface density of the one or more heat exchangers tied to the power gearbox of the turbofan engine and a heat conductance factor.

The resultant heat transfer surface density of the one or more heat exchangers measures the resultant compactness of the one or more heat exchangers. The resultant heat transfer surface area density for a selected architecture is determined by taking a product to an Nth root, wherein the product is determined by multiplying together a heat transfer surface area density associated with each of the one or more heat exchangers tied to the power gearbox, wherein N is a number of heat exchangers tied to the power gearbox. The heat transfer surface area density for a given heat exchanger is a function of the heat transfer surface area and volume of the channels of the given heat exchanger. In this regard, the heat transfer surface area density for a given heat exchanger is based on the architecture of the given heat exchanger.

The heat conductance factor, as noted above, relates the power gearbox heat load associated with the power gearbox, the fan power consumption function associated with the fan, the fan diameter, and the bypass ratio of the turbofan engine. In this regard, the heat conductance factor is based on the architecture of the power gearbox as well as the turbofan engine. The greater the power gearbox heat load and/or the larger the fan diameter, the greater the heat conductance factor. The greater the bypass ratio and/or fan power consumption function, the smaller the heat conductance factor. Greater heat transfer surface area density and/or heat conductance factor leads to increased heat exchanger capacity, which results in higher potential to process more heat duty associated with the power gearbox.

Moreover, as engine designers continue to pursue more fuel-efficient and quieter turbofan engines that emit less carbon dioxide, engine designers have pushed toward geared turbofan engines with higher bypass ratios, gear ratios, and gearbox heat loads-implying higher thrust. This indicates that heat exchangers with high heat transfer surface area density values may be useful in processing the heat duty of a power gearbox of a turbofan engine. The combination of higher resultant heat transfer surface area density and heat conductance factor leads to higher heat exchanger capacity, and thus, higher potential for the one or more heat exchangers to process more heat duty associated with the power gearbox. Accordingly, one or more heat exchangers having a heat exchanger capacity within a range specified herein can identify a more optimal configuration for processing the heat duty associated with a power gearbox of a turbofan engine.

Particularly, the ranges of heat exchanger capacities for one or more heat exchangers tied to a power gearbox noted herein reflect the inventors' work done to identify optimal structures for the one or more heat exchangers, power gearboxes, and turbofan engines that take into consideration various benefits and penalties of choosing one structural architecture of one or more heat exchangers and turbofan engine over another. In this regard, as discovered by the inventors, the ranges of heat exchanger capacities provided herein strike a balance between the compactness and weight of one or more heat exchangers tied to a power gearbox, the ability of the one or more heat exchangers to process the heat duty of the power gearbox, the susceptibility of the channels of the one or more heat exchangers to becoming blocked or contaminated, the manufacturability of the one or more heat exchangers, the manufacturability of the power gearbox, gearbox efficiency, the manufacturability of the turbofan engine, and the thrust and speed outputs of the turbofan engine. Accordingly, one or more heat exchangers having a heat exchanger capacity within a range specified herein can ensure that the architecture of the one or more heat exchangers tied to the power gearbox and the architecture of the turbofan engine are such that the one or more heat exchangers are optimally compact and effective at processing the heat duty of the power gearbox.

The inventors also found a relationship between the heat exchanger capacity of one or more heat exchangers tied to a power gearbox of a turbofan engine and a rotational speed of the low pressure spool mechanically coupled with the power gearbox. The inventors have observed that, as a maximum rotational speed of the low pressure spool of a given turbofan increases, the heat exchanger capacity exponentially decreases. This discovered relationship can be used advantageously to design geared turbofan engines and their associated power gearbox and heat exchangers, since the relationship accounts for operational characteristics of the engine that influence the heat exchanger capacity.

Further, utilizing the heat exchanger capacity, the inventors found that the number of suitable or feasible engine and/or heat exchanger designs that allow the heat exchanger to meet compactness, weight, and heat duty requirements could be greatly diminished, thereby facilitating a more rapid down selection of designs to consider as a turbofan engine having one or more heat exchangers tied to a power gearbox is developed. Such a benefit provides more insight into the requirements for a given turbofan engine well before specific technologies, integration and system requirements are developed fully. It may also prevent late-stage redesign. For instance, selection of a heat exchanger's heat transfer surface area density may be facilitated by utilizing a heat exchanger capacity within the ranges provided herein, which may help determine the needed channel diameters and wall thickness of the core of the heat exchanger. Moreover, utilizing a heat exchanger capacity within the ranges provided herein may eliminate or otherwise reduce implementation of heat exchangers having heat transfer surface area density values that are too high, making them not practical to manufacture. Higher heat transfer surface area density values may create higher susceptibility to blocking/contamination of the exchanger channels, which may limit the heat exchanger's effectiveness. Also, utilizing a heat exchanger capacity within the ranges provided herein may facilitate exclusion or reduction of heat exchangers that are bulky.

With reference now to FIGS. 1, 2, 3, 4, and 5 , FIG. 5 lists various relationships between heat exchanger characteristics and operational and architectural characteristics of a turbofan engine to be described below. Notably, the turbofan engine 100 and the one or more heat exchangers 192 are arranged so that the one or more heat exchangers 192 in flow communication with the power gearbox 142 have a heat exchanger capacity HEC. Generally, the heat exchanger capacity HEC measures the heat load capacity on the heat exchangers 192 tied to the power gearbox 142 of the turbofan engine 100. The heat exchangers 192 are tied to the power gearbox 142 in that the one or more heat exchangers are configured to process at least a portion of a heat load of the power gearbox 142. The heat exchanger capacity HEC is a dimensionless quantity that relates a resultant heat transfer surface area density HTSAD_(R) associated with the one or more heat exchangers 192 tied to the power gearbox 142 and a heat conductance factor HCF.

As will be explained more fully below, the resultant heat transfer surface area density HTSAD_(R) is a function of the structural architecture of the one or more heat exchangers 192 tied to the power gearbox 142. The heat conductance factor HCF is a function of certain aspects of the one or more heat exchangers 192 and the turbofan engine 100. Specifically, the heat conductance factor HCF relates a power gearbox heat load Q_(GB) associated with the one or more heat exchangers 192, a fan power consumption function P_(FAN) associated with the fan 134, a fan diameter D_(FAN) of the fan 134, and a bypass ratio BPR of the turbofan engine 100.

The heat exchanger capacity HEC is defined as a product determined by multiplying the resultant heat transfer surface area density HTSAD_(R) by the heat conductance factor HCF. Stated differently, the heat exchanger capacity HEC is the product of the resultant heat transfer surface area density HTSAD_(R) and the heat conductance factor HCF. The heat exchanger capacity HEC is defined by the inventors as follows: HEC=HTSAD_(R)*HCF  (1)

The resultant heat transfer surface area density HTSAD_(R) of (1) provides a measure of the resultant compactness of the one or more heat exchangers 192 tied to the power gearbox 142. The unit of measure for the resultant heat transfer surface area density HTSAD_(R) is meters squared per meters cubed (m²/m³). The resultant heat transfer surface area density HTSAD_(R) is determined by taking a product to an Nth root, wherein the product is determined by multiplying together a heat transfer surface area density associated with each of the one or more heat exchangers 192 tied to the power gearbox 142, and N is a number of heat exchangers tied to the power gearbox 142. The resultant heat transfer surface area density HTSAD_(R) is defined by the inventors according to (2), wherein i is an index starting at 1, N is the number of heat exchangers tied to the power gearbox 142, and HTSAD is the heat transfer surface area density associated with a given heat exchanger HX:

$\begin{matrix} {{HTSAD}_{R} = \left( {{HTSAD}_{HXi}*{HTSAD}_{{HXi} + 1}*{HTSAD}_{{HXi} + 2}*\ldots{HTSAD}_{HXN}} \right)^{\frac{1}{N}}} & (2) \end{matrix}$

By way of example, for the depicted embodiment of FIG. 1 , there are four (4) heat exchangers 192 tied to the power gearbox 142. Thus, the number of heat exchangers N is four (4). Consequently, the product determined by multiplying together the heat transfer surface area densities HTSAD associated with the heat exchangers 192 is thus raised to a quarter power (¼), or taken to a fourth root. For the embodiment of FIG. 1 , (2) can be rewritten as shown in (2.1) set forth below:

$\begin{matrix} {{HTSAD}_{R} = \left( {{HTSAD}_{{HX}1}*{HTSAD}_{{HX}2}*{HTSAD}_{{HX}3}*{HTSAD}_{{HX}4}} \right)^{\frac{1}{4}}} & (2.1) \end{matrix}$ wherein the first heat exchanger 192A corresponds with HX1, the second heat exchanger 192B corresponds with HX2, the third heat exchanger 192C corresponds with HX3, and the fourth heat exchanger 192D corresponds with HX4. Alternatively, for the depicted embodiment of FIG. 1 , (2) can be rewritten in root form in accordance with (2.2) set forth below:

$\begin{matrix} {{HTSAD}_{R} = \sqrt[4]{\left( {{HTSAD}_{{HX}1}*{HTSAD}_{{HX}2}*{HTSAD}_{{HX}3}*{HTSAD}_{{HX}4}} \right)}} & (2.2) \end{matrix}$

The heat transfer surface area density HTSAD for a given heat exchanger provides a measure of the compactness of the given heat exchanger. The heat transfer surface area density HTSAD for a given heat exchanger is defined as a quotient determined by dividing a heat exchanger channel surface area A_(HT) associated with a plurality of channels of the given heat exchanger by a heat exchanger channel volume V_(HT) associated with the plurality of channels of the given heat exchanger. Stated differently, the heat exchanger channel surface area A_(HT) divided by the heat exchanger channel volume V_(HT) is equal to the heat transfer surface area density HTSAD for a given heat exchanger.

The heat exchanger channel surface area A_(HT) for a given heat exchanger is defined by a surface area of the channels of the given heat exchanger. The heat exchanger channel volume V_(HT) for the given heat exchanger is defined by a volume of the channels of the given heat exchanger. In this regard, the heat transfer surface area density HTSAD for a given heat exchanger relates the surface area of the channels with the volume of the channels. The unit of measure for the heat transfer surface area density HTSAD for a given heat exchanger is meters squared per meters cubed (m²/m³). The heat transfer surface area density HTSAD for a given heat exchanger is defined by the inventors as follows: HTSAD=A _(HT) /V _(HT)  (3)

The heat exchanger channel surface area A_(HT) for a given heat exchanger may be determined as follows. First, the surface area associated with each channel of each core of the heat exchanger is determined. Second, once the surface area associated with each channel of the given heat exchanger is determined, the surface area for each channel is summed to determine the heat exchanger channel surface area A_(HT). In this regard, the heat exchanger channel surface area A_(HT) describes the total surface area associated with the channels of the core of each exchanger unit of the heat exchanger.

By way of example, the heat exchanger channel surface area A_(HT) for the first heat exchanger 192A, or HX1 from (2.1) and (2.2), may be determined as follows. First, the surface area associated with each channel 241, 242 of each core 240 of the first heat exchanger 192A is determined. The surface area for a given one of the channels 241, 242 may be defined as a circumference C1 (see FIG. 4 depicting a circumference of one of the second channels 242) of the given channel multiplied by a length L1 (FIG. 3 ) of the given channel. As will be appreciated, the circumference C1 of the given channel may be defined as the diameter D1 (see FIG. 4 depicting a diameter of one of the second channels 242) of the given channel multiplied by Pi (π). Second, once the surface area associated with each channel 241, 242 of the core 240 of each exchanger unit 210 of the first heat exchanger 192A is determined, the surface area for each channel 241, 242 is summed to determine the heat exchanger channel surface area A_(HT). In this regard, the heat exchanger channel surface area A_(HT) describes the total surface area associated with the channels 241, 242 of the core 240 of each exchanger unit 210 of the first heat exchanger 192A. The heat exchanger channel surface area A_(HT) for the other heat exchangers 192B, 192C, 192D can be determined in a same manner as described above.

The heat exchanger channel volume V_(HT) for a given heat exchanger may be determined as follows. First, the volume associated with each channel of each core of the heat exchanger is determined. Second, once the volume associated with each channel of the heat exchanger is determined, the volume for each channel is summed to determine the heat exchanger channel volume V_(HT). In this regard, the heat exchanger channel volume V_(HT) describes the total volume associated with the channels of the core of each exchanger unit of the heat exchanger.

By way of example, the heat exchanger channel volume V_(HT) for the first heat exchanger 192A, or HX1 from (2.1) and (2.2), may be determined as follows. First, the volume associated with each channel 241, 242 of each core 240 of the first heat exchanger 192A is determined. The volume for a given one of the channels 241, 242 may be defined as an area A1 of the given channel (represented in FIG. 4 by the cross hatching in one of the first channels 241) multiplied by the length L1 of the given channel. As will be appreciated, the area A1 of the given channel may be defined as the diameter D1 squared multiplied by Pi (w) multiplied by one quarter, or stated differently, the radius of the given channel squared multiplied by Pi (w). Second, once the volume associated with each channel 241, 242 of the core 240 of each exchanger unit 210 of the first heat exchanger 192A is determined, the volume for each channel 241, 242 is summed to determine the heat exchanger channel volume V_(HT). In this regard, the heat exchanger channel volume V_(HT) describes the total volume associated with the channels 241, 242 of the core 240 of each exchanger unit 210 of the first heat exchanger 192A. The heat exchanger channel volume V_(HT) for the other heat exchangers 192B, 192C, 192D can be determined in a same manner as described above.

The heat transfer surface area density HTSAD associated with the first heat exchanger 192A, or HTSAD_(HX1) of (2.1) and (2.2), may thus be determined as the quotient determined by dividing the heat exchanger channel surface area A_(HT) associated with the plurality of channels 241, 242 of the first heat exchanger 192A to the heat exchanger channel volume V_(HT) associated with the plurality of channels 241, 242 of the first heat exchanger 192A. Likewise, the heat transfer surface area density HTSAD associated with the second heat exchanger 192B, or HTSAD_(HX2) of (2.1) and (2.2), may thus be determined as the quotient determined by dividing the heat exchanger channel surface area A_(HT) associated with the plurality of channels of the second heat exchanger 192B to the heat exchanger channel volume V_(HT) associated with the plurality of channels of the second heat exchanger 192B. Further, the heat transfer surface area density HTSAD associated with the third heat exchanger 192C, or HTSAD_(HX3) of (2.1) and (2.2), may therefore be determined as the quotient determined by dividing the heat exchanger channel surface area A_(HT) associated with the plurality of channels of the third heat exchanger 192C to the heat exchanger channel volume V_(HT) associated with the plurality of channels of the third heat exchanger 192C. Moreover, the heat transfer surface area density HTSAD associated with the fourth heat exchanger 192D, or HTSAD_(HX4) of (2.1) and (2.2), may thus be determined as the quotient determined by dividing the heat exchanger channel surface area A_(HT) associated with the plurality of channels of the fourth heat exchanger 192D to the heat exchanger channel volume V_(HT) associated with the plurality of channels of the fourth heat exchanger 192D.

The heat conductance factor HCF of (1) describes the degree of difficulty in transferring thermal energy from the power gearbox 142 to the one or more heat exchangers 192 based on the power gearbox heat load Q_(GB), the fan power consumption function P_(FAN), the fan diameter D_(FAN), and the bypass ratio BPR. Stated differently, the heat conductance factor HCF represents the ease of heat load distribution to the one or more heat exchangers 192 tied to the power gearbox 142. Larger fan diameters and lower bypass ratios may provide more airflow supply, implying higher potential for heat transfer. Higher power gearbox heat loads and lower fan power consumption implies higher heat load availability to be processed by the one or more heat exchangers 192.

The heat conductance factor HCF is defined as a product determined by multiplying by a first quotient by a second quotient. The first quotient is determined by dividing the power gearbox heat load Q_(GB) by the fan power consumption function P_(FAN). The second quotient is determined by dividing a fan diameter D_(FAN) of the fan 134 by a bypass ratio BPR of the turbofan engine 100. In this regard, the heat conductance factor HCF relates the power gearbox heat load Q_(GB) associated with the one or more heat exchangers 192, the fan power consumption function P_(FAN) associated with the fan 134, the fan diameter D_(FAN) of the fan 134, and the bypass ratio BPR of the turbofan engine 100. The unit of measure for the heat conductance factor HCF is meters (m). The heat conductance factor HCF is defined by the inventors as follows: HCF=(Q _(GB) /P _(FAN))*(D _(FAN)/BPR)  (4)

The power gearbox heat load Q_(GB) associated with the first quotient of (4) is defined as a product determined by multiplying a maximum continuous thrust T_(Max. Cont.) associated with the turbofan engine 100 by one (1) minus a power gearbox efficiency η_(GB) and by a maximum continuous cruise speed V_(Cruise) associated with the turbofan engine 100. The maximum continuous thrust T_(Max. Cont.) is a maximum continuous thrust produced by the turbofan engine 100, or rather, a maximum thrust the turbofan engine 100 can produce continuously. The maximum continuous cruise speed V_(Cruise) is a maximum continuous speed at which the turbofan engine 100 can operate during cruise flight, or rather, a maximum speed at which the turbofan engine 100 can achieve continuously during cruise flight. As used herein, cruise flight refers to a phase of flight in which an aircraft levels in altitude after a climb phase and prior to descending to an approach phase. In various examples, cruise flight may take place at a cruise altitude up to approximately 65,000 ft. In certain examples, cruise altitude is between approximately 28,000 ft. and approximately 45,000 ft. In yet other examples, cruise altitude is expressed in flight levels (FL) based on a standard air pressure at sea level, in which cruise flight is between FL280 and FL650. In another example, cruise flight is between FL280 and FL450. In still certain examples, cruise altitude is defined based at least on a barometric pressure, in which cruise altitude is between approximately 4.85 psia and approximately 0.82 psia based on a sea-level pressure of approximately 14.70 psia and sea-level temperature at approximately 59 degrees Fahrenheit. In another example, cruise altitude is between approximately 4.85 psia and approximately 2.14 psia. It should be appreciated that, in certain examples, the ranges of cruise altitude defined by pressure may be adjusted based on a different reference sea-level pressure and/or sea-level temperature.

As the power gearbox heat load Q_(GB) is based on the maximum continuous thrust T_(Max. Cont.) and the maximum continuous cruise speed V_(Cruise) associated with the turbofan engine 100, the power gearbox heat load Q_(GB) can be deemed a maximum continuous heat load, or rather, a maximum heat load the power gearbox 142 can generate continuously. It should be noted that the maximum continuous heat load is different than the absolute maximum heat load the power gearbox 142 can generate, e.g., during takeoff.

In some embodiments, the power gearbox efficiency η_(GB) of the power gearbox 142 is between 99.2 and 99.8. The unit of measure for the maximum continuous thrust T_(Max. Cont.) is kilonewtons (kN). The unit of measure for the maximum cruise speed V_(Cruise) is meters per second (m/s). The power gearbox efficiency η_(GB) is a dimensionless quantity. The power gearbox heat load Q_(GB) is defined by the inventors as follows: Q _(GB) =T _(Max. Cont.)*(1−η_(GB))*V _(Cruise)  (5)

The fan power consumption function P_(FAN) associated with the first quotient of (4) is defined as a product determined by multiplying a fan thrust function T_(FAN) by the maximum cruise speed V_(Cruise) associated with the turbofan engine 100. The unit of measure for the fan power consumption function P_(FAN) is megawatts (MW). The fan power consumption function P_(FAN) is defined by the inventors as follows: P _(FAN) =T _(FAN) *V _(Cruise)  (6)

The fan thrust function T_(FAN) is defined as a product determined by multiplying an air density ρ_(Air) of air at 11,000 meters (m) above sea level by a fan tip speed V_(Tip Speed), squared, by a fan area A_(FAN) of the fan 134. The unit of measure for the air density ρ_(Air) is kilograms per meters cubed (kg/m³). The unit of measure for the fan thrust function T_(FAN) is kilonewtons (kN). The fan thrust function T_(FAN) is defined by the inventors as follows: T _(FAN)=ρ_(Air) *V _(Tip speed) ² *A _(FAN)  (7)

The fan tip speed V_(Tip Speed) is defined as a product determined by multiplying Pi (π) by a fan diameter D_(FAN) of the fan 134 by a quotient, the quotient being determined by dividing a rotational speed N1 of the low pressure spool 133 by a gear ratio GR of the power gearbox 142. The unit of measure for the fan tip speed V_(Tip Speed) is meter per second (m/s). The fan tip speed V_(Tip Speed) is a maximum continuous fan speed, or rather, a maximum fan tip speed at which the fan 134 can be held continuously. The unit of measure for the fan diameter D_(FAN) is meters (m). The unit of measure for the rotational speed N1 of the low pressure spool 133 is revolutions per minute (RPM). The gear ratio GR of the power gearbox 142 is a dimensionless value. The fan tip speed V_(Tip Speed) is defined by the inventors as follows: V _(Tip Speed) =π*D _(FAN)*(N1/GR)  (8)

The fan diameter D_(FAN) is defined as a distance spanning between a leading edge tip of one fan blade 136 to a leading edge tip of a radially opposite fan blade 136. Stated another way, the fan diameter D_(FAN) is defined as a fan radius R_(FAN) multiplied by two, or stated another way, as D_(FAN)=R_(FAN)*2, wherein the fan radius R_(FAN) spans from the longitudinal centerline 102 to a leading edge tip of one of the fan blades 136. In some example embodiments, the fan diameter D_(FAN) of the fan 134 of the turbofan engine 100 is between 0.7 m and 3.5 m. In other example embodiments, the fan diameter D_(FAN) of the fan 134 of the turbofan engine 100 is between 1.8 m and 3.5 m. In instances in which the fan section 104 includes a plurality of fan stages, the fan diameter D_(FAN) is to be determined based on the fan having the largest fan diameter.

The fan area A_(FAN) is defined as a quotient determined by dividing a product by four, wherein the product is determined by multiplying Pi (w) by the fan diameter D_(FAN) of the fan 134, squared. The unit of measure for the fan area A_(FAN) is meters squared (m²). The fan area A_(FAN) is defined according to (9): A _(FAN)=(π*D _(Fan) ²)/4  (9)

The fan diameter D_(FAN) associated with the second quotient of (4) is defined as noted above.

The bypass ratio BPR associated with the second quotient of (4) is defined by the inventors as a ratio of a mass flow rate of the first portion of air 158 flowing through the bypass passage 152 to a mass flow rate of the second portion of air 160 entering the engine core 106 through the core inlet 110. In some example embodiments, the bypass ratio BPR of the turbofan engine 100 may be between three and twenty (3-20). In other example embodiments, the bypass ratio BPR of the turbofan engine 100 may be between three and ten (3-10). In further example embodiments, the bypass ratio BPR of the turbofan engine 100 may be between ten and twenty (10-20).

In some embodiments, the heat exchanger capacity HEC is between 0.77 and 48.0 for a rotational speed N1 of the low pressure spool 133 between 2,000 and 16,000 revolutions per minute (RPM) at one hundred percent (100%) capacity and a resultant heat transfer surface area density HTSAD_(R) being between 3,000 m²/m³ and 13,000 m²/m³. FIG. 6 graphically depicts the heat exchanger capacity HEC as a function of the rotational speed N1 of the low pressure spool 133 for such example embodiments.

In yet other embodiments, the heat exchanger capacity HEC is between 6.17 and 48.0 for a rotational speed N1 of the low pressure spool 133 between 2,000 and 16,000 revolutions per minute (RPM) at one hundred percent (100%) capacity and a resultant heat transfer surface area density HTSAD_(R) being between 6,000 m²/m³ and 13,000 m²/m³. FIG. 7 graphically depicts the heat exchanger capacity HEC as a function of the rotational speed N1 of the low pressure spool 133 for such example embodiments.

In some further embodiments, the heat exchanger capacity HEC is between 0.77 and 22.02 for a rotational speed N1 of the low pressure spool 133 between 2,000 and 16,000 revolutions per minute (RPM) at one hundred percent (100%) capacity and a resultant heat transfer surface area density HTSAD_(R) being between 3,000 m²/m³ and 6,000 m²/m³. FIG. 8 graphically depicts the heat exchanger capacity HEC as a function of the rotational speed N1 of the low pressure spool 133 for such example embodiments.

In yet other embodiments, the heat exchanger capacity HEC is between 8.23 and 48.0 for a rotational speed N1 of the low pressure spool 133 between 2,000 and 10,000 revolutions per minute (RPM) at one hundred percent (100%) capacity and a resultant heat transfer surface area density HTSAD_(R) being between 6,000 m²/m³ and 13,000 m²/m³. FIG. 9 graphically depicts the heat exchanger capacity HEC as a function of the rotational speed N1 of the low pressure spool 133 for such example embodiments.

In some further embodiments, the heat exchanger capacity HEC is between 6.17 and 17.84 for a rotational speed N1 of the low pressure spool 133 between 10,000 and 16,000 revolutions per minute (RPM) at one hundred percent (100%) capacity and a resultant heat transfer surface area density HTSAD_(R) being between 6,000 m²/m³ and 13,000 m²/m³. FIG. 10 graphically depicts the heat exchanger capacity HEC as a function of the rotational speed N1 of the low pressure spool 133 for such example embodiments.

In some embodiments, the heat exchanger capacity HEC is between 1.03 and 22.02 for a rotational speed N1 of the low pressure spool 133 between 2,000 and 10,000 revolutions per minute (RPM) at one hundred percent (100%) capacity and a resultant heat transfer surface area density HTSAD_(R) being between 3,000 m²/m³ and 6,000 m²/m³. FIG. 11 graphically depicts the heat exchanger capacity HEC as a function of the rotational speed N1 of the low pressure spool 133 for such example embodiments.

In other embodiments, the heat exchanger capacity HEC is between 0.77 and 8.23 for a rotational speed N1 of the low pressure spool 133 between 10,000 and 16,000 revolutions per minute (RPM) at one hundred percent (100%) capacity and a resultant heat transfer surface area density HTSAD_(R) being between 3,000 m²/m³ and 6,000 m²/m³. FIG. 12 graphically depicts the heat exchanger capacity HEC as a function of the rotational speed N1 of the low pressure spool 133 for such example embodiments.

With reference now to FIG. 13 , various examples of turbofan engines each having one or more heat exchangers tied to a power gearbox of the turbofan engine are provided below.

EXAMPLE 1: In a first example, a turbofan engine includes one or more heat exchangers tied to a power gearbox. The power gearbox mechanically couples a low pressure spool with a fan of the turbofan engine. The one or more heat exchangers are arranged such that the resultant heat transfer surface area density HTSAD_(R) is 3,000 m²/m³. Further, for the first example, the fan has a fan diameter D_(FAN) of 3.5 m. The turbofan engine defines a bypass ratio BPR of 3.0. The power gearbox has a gear ratio of 1.2. The power gearbox efficiency of the power gearbox is 99.2%. The turbofan engine is further arranged so that the maximum continuous thrust is 50 kN and a rotational speed of the low pressure spool of the turbofan engine is 3,000 RPM at one hundred percent (100%) capacity. Thus, the heat conductance factor is 0.00078 m. Accordingly, for the first example, the heat exchanger capacity HEC is 2.33.

EXAMPLE 2: In a second example, a turbofan engine includes one or more heat exchangers tied to a power gearbox. The power gearbox mechanically couples a low pressure spool with a fan of the turbofan engine. The one or more heat exchangers are arranged such that the resultant heat transfer surface area density HTSAD_(R) is 6,000 m²/m³. Further, for the second example, the fan has a fan diameter D_(FAN) of 2.5 m. The turbofan engine defines a bypass ratio BPR of 10.0. The power gearbox has a gear ratio of 3.5. The power gearbox efficiency of the power gearbox is 99.5%. The turbofan engine is further arranged so that the maximum continuous thrust is 200 kN and a rotational speed of the low pressure spool of the turbofan engine is 8,000 RPM at one hundred percent (100%) capacity. Thus, the heat conductance factor is 0.00191 m. Accordingly, for the second example, the heat exchanger capacity HEC is 11.46.

EXAMPLE 3: In a third example, a turbofan engine includes one or more heat exchangers tied to a power gearbox. The power gearbox mechanically couples a low pressure spool with a fan of the turbofan engine. The one or more heat exchangers are arranged such that the resultant heat transfer surface area density HTSAD_(R) is 10,000 m²/m³. Further, for the third example, the fan has a fan diameter D_(FAN) of 1.7 m. The turbofan engine defines a bypass ratio BPR of 15.0. The power gearbox has a gear ratio of 4.0. The power gearbox efficiency of the power gearbox is 99.7%. The turbofan engine is further arranged so that the maximum continuous thrust is 400 kN and a rotational speed of the low pressure spool of the turbofan engine is 13,000 RPM at one hundred percent (100%) capacity. Thus, the heat conductance factor is 0.002404 m. Accordingly, for the third example, the heat exchanger capacity HEC is 24.04.

EXAMPLE 4: In a fourth example, in a fourth example, a turbofan engine includes one or more heat exchangers tied to a power gearbox. The power gearbox mechanically couples a low pressure spool with a fan of the turbofan engine. The one or more heat exchangers are arranged such that the resultant heat transfer surface area density HTSAD_(R) is 13,000 m²/m³. Further, for the fourth example, the fan has a fan diameter D_(FAN) of 1.4 m. The turbofan engine defines a bypass ratio BPR of 20.0. The power gearbox has a gear ratio of 5.0. The power gearbox efficiency of the power gearbox is 99.8%. The turbofan engine is further arranged so that the maximum continuous thrust is 600 kN and a rotational speed of the low pressure spool of the turbofan engine is 16,000 RPM at one hundred percent (100%) capacity. Thus, the heat conductance factor is 0.00333 m. Accordingly, for the fourth example, the heat exchanger capacity HEC is 43.29.

FIG. 14 provides a flow diagram for a method 300 of operating a turbofan engine having one or more heat exchangers tied to a power gearbox of the turbofan engine. The turbofan engine can be mounted to an aircraft, for example.

At 302, the method 300 includes operating a turbofan engine having a low pressure spool, a fan, a power gearbox mechanically coupling the low pressure spool and the fan, and one or more heat exchangers tied to the power gearbox, and wherein the one or more heat exchangers have a heat exchanger capacity defined by a resultant heat transfer surface area density associated with the one or more heat exchangers multiplied by a heat conductance factor that relates a power gearbox heat load associated with the one or more heat exchangers, a fan power consumption function of the fan, a fan diameter of the fan, and a bypass ratio of the turbofan engine, and wherein the heat exchanger capacity is between 0.77 and 48 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent (100%) capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 13,000 m²/m³. The heat exchanger capacity according to such implementations is graphically represented in FIG. 6 .

In some implementations, the heat exchanger capacity is between 6.17 and 48.0 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent (100%) capacity and a resultant heat transfer surface area density being between 6,000 m²/m³ and 13,000 m²/m³. The heat exchanger capacity according to such implementations is graphically represented in FIG. 7 .

In some other implementations, the heat exchanger capacity is between 0.77 and 22.02 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent (100%) capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 6,000 m²/m³. The heat exchanger capacity according to such implementations is graphically represented in FIG. 8 .

In some further implementations, the resultant heat transfer surface area density is determined by taking a product to an Nth root, wherein the product is determined by multiplying a heat transfer surface area density associated with each of the one or more heat exchangers tied to the power gearbox together, wherein N is a number of heat exchangers tied to the power gearbox. In such implementations, the heat transfer surface area density for a given one of the one or more heat exchangers is defined as a quotient determined by dividing a heat exchanger channel surface area associated with a plurality of channels of the given one of the one or more heat exchangers to a heat exchanger channel volume associated with the plurality of channels of the given one of the one or more heat exchangers. Accordingly, a heat transfer surface area density is determined for each heat exchanger tied to power gearbox, and these heat transfer surface area densities are multiplied together to determine the product. The product is then taken to the Nth root to determine the resultant heat transfer surface area density.

In some implementations, the heat conductance factor is defined as a product determined by multiplying a first quotient by a second quotient, the first quotient being determined by dividing the power gearbox heat load by the fan power consumption function, the second quotient being determined by dividing the fan diameter by the bypass ratio of the turbofan engine.

The parameters of the heat conductance factor are defined by the inventors as follows. The power gearbox heat load, or heat generation, is defined as a product determined by multiplying a maximum continuous thrust associated with the turbofan engine by one minus a power gearbox efficiency of the power gearbox and by a maximum continuous cruise speed associated with the turbofan engine. In such implementations, the power gearbox efficiency is between 99.2 and 99.8. The fan power consumption function is defined as a product determined by multiplying a fan thrust function by a maximum cruise speed associated with the turbofan engine. The fan thrust function is defined as a product determined by multiplying an air density of air at 11,000 m above sea level by a fan tip speed of the fan, squared, by an area of the fan. The fan area is defined as a quotient determined by dividing a product by four, wherein the product is determined by multiplying Pi (w) by a fan diameter of the fan, squared. The fan tip speed of the fan is defined as a product determined by multiplying Pi (w) by a fan diameter of the fan by a quotient, the quotient being determined by dividing a rotational speed of the low pressure spool by a gear ratio of the power gearbox.

The fan diameter of the fan may be defined as a distance spanning between a leading edge tip of one fan blade of the fan to a leading edge tip of a radially opposite fan blade. Stated another way, the fan diameter may be defined as a fan radius multiplied by two, wherein the fan radius spans from the longitudinal centerline of the turbofan engine to a leading edge tip of one of the fan blades. The bypass ratio of a turbofan engine is defined by a ratio of a mass flow rate of a first portion of air flowing through a bypass passage to a mass flow rate of a second portion of air entering the engine core through the core inlet.

In some implementations, the one or more heat exchangers tied to the power gearbox include a fuel-to-oil heat exchanger, an air-to-oil heat exchanger, and an oil-to-oil heat exchanger. In some implementations, the one or more heat exchangers tied to the power gearbox include at least one of each of a fuel-to-oil heat exchanger, an air-to-oil heat exchanger, and an oil-to-oil heat exchanger, and at least two of one of the fuel-to-oil heat exchanger, the air-to-oil heat exchanger, and the oil-to-oil heat exchanger.

In some implementations, the one or more heat exchangers include at least four (4) heat exchangers. In some implementations, the one or more heat exchangers include at least three (3) heat exchangers. In some implementations, the one or more heat exchangers include at least two (2) heat exchangers. In some implementations, the one or more heat exchangers include one (1) heat exchanger. In some implementations, the one or more heat exchangers include between four (4) and ten (10) heat exchangers.

Although specific features of various embodiments may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the present disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.

This written description uses examples to disclose the present disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Further aspects are provided by the subject matter of the following clauses:

A turbofan engine, comprising: a low pressure spool; a fan; a power gearbox mechanically coupling the low pressure spool and the fan; and one or more heat exchangers tied to the power gearbox, the one or more heat exchangers having a heat exchanger capacity defined by a resultant heat transfer surface area density associated with the one or more heat exchangers multiplied by a heat conductance factor that relates a power gearbox heat load, a fan power consumption function, a fan diameter of the fan, and a bypass ratio of the turbofan engine, and wherein the heat exchanger capacity is between 0.77 and 48 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 13,000 m²/m³.

The turbofan engine of any preceding clause, wherein the resultant heat transfer surface area density is determined by taking a product to an Nth root, wherein the product is determined by multiplying a heat transfer surface area density associated with each of the one or more heat exchangers tied to the power gearbox together, wherein N is a number of heat exchangers tied to the power gearbox.

The turbofan engine of any preceding clause, wherein the one or more heat exchangers each have one or more exchanger units each having a core defining a plurality of channels.

The turbofan engine of any preceding clause, wherein the heat transfer surface area density for a given one of the one or more heat exchangers is defined as a quotient determined by dividing a heat exchanger channel surface area associated with the plurality of channels of the given one of the one or more heat exchangers to a heat exchanger channel volume associated with the plurality of channels of the given one of the one or more heat exchangers.

The turbofan engine of any preceding clause, wherein the heat conductance factor is defined as a product determined by multiplying a first quotient by a second quotient, the first quotient being determined by dividing the power gearbox heat load by the fan power consumption function, the second quotient being determined by dividing the fan diameter of the fan by the bypass ratio of the turbofan engine, wherein the power gearbox heat load is defined as a product determined by multiplying a maximum continuous thrust associated with the turbofan engine by one minus a power gearbox efficiency of the power gearbox and by a maximum continuous cruise speed associated with the turbofan engine, and wherein the fan power consumption function is defined as a product determined by multiplying a fan thrust function by a maximum cruise speed associated with the turbofan engine.

The turbofan engine of any preceding clause, wherein the power gearbox efficiency is between 99.2 and 99.8.

The turbofan engine of any preceding clause, wherein the fan thrust function is defined as a product determined by multiplying an air density of air at 11,000 m above sea level by a fan tip speed of the fan, squared, by a fan area of the fan, wherein the fan area is defined as a quotient determined by dividing a product by four, wherein the product is determined by multiplying pi by the fan diameter of the fan, squared, and wherein the fan tip speed of the fan is defined as a product determined by multiplying pi by the fan diameter of the fan by a quotient, the quotient being determined by dividing a rotational speed of the low pressure spool by a gear ratio of the power gearbox.

The turbofan engine of any preceding clause, wherein the heat exchanger capacity is between 6.17 and 48.0 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 6,000 m²/m³ and 13,000 m²/m³.

The turbofan engine of any preceding clause, wherein the heat exchanger capacity is between 0.77 and 22.02 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 6,000 m²/m³.

The turbofan engine of any preceding clause, wherein the heat exchanger capacity is between 8.23 and 48.0 for a rotational speed of the low pressure spool between 2,000 and 10,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 6,000 m²/m³ and 13,000 m²/m³.

The turbofan engine of any preceding clause, wherein the heat exchanger capacity is between 6.17 and 17.84 for a rotational speed of the low pressure spool between 10,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 6,000 m²/m³ and 13,000 m²/m³.

The turbofan engine of any preceding clause, wherein the heat exchanger capacity is between 1.03 and 22.02 for a rotational speed of the low pressure spool between 2,000 and 10,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 6,000 m²/m³.

The turbofan engine of any preceding clause, wherein the heat exchanger capacity is between 0.77 and 8.23 for a rotational speed of the low pressure spool between 10,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 6,000 m²/m³.

The turbofan engine of any preceding clause, wherein the one or more heat exchangers include a fuel-to-oil heat exchanger, an air-to-oil heat exchanger, and an oil-to-oil heat exchanger.

The turbofan engine of any preceding clause, wherein the one or more heat exchangers include at least four heat exchangers.

A method, comprising: operating a turbofan engine having a low pressure spool, a fan, a power gearbox mechanically coupling the low pressure spool and the fan, and one or more heat exchangers tied to the power gearbox, and wherein the one or more heat exchangers have a heat exchanger capacity defined by a resultant heat transfer surface area density associated with the one or more heat exchangers multiplied by a heat conductance factor that relates a power gearbox heat load associated with the one or more heat exchangers, a fan power consumption function of the fan, a fan diameter of the fan, and a bypass ratio of the turbofan engine, and wherein the heat exchanger capacity is between 0.77 and 48 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 13,000 m²/m³.

The method of any preceding clause, wherein the resultant heat transfer surface area density is determined by taking a product to an Nth root, wherein the product is determined by multiplying a heat transfer surface area density associated with each of the one or more heat exchangers tied to the power gearbox together, wherein N is a number of heat exchangers tied to the power gearbox, the heat transfer surface area density for a given one of the one or more heat exchangers is defined as a quotient determined by dividing a heat exchanger channel surface area associated with a plurality of channels of the given one of the one or more heat exchangers to a heat exchanger channel volume associated with the plurality of channels of the given one of the one or more heat exchangers, and wherein the heat conductance factor is defined as a product determined by multiplying a first quotient by a second quotient, the first quotient being determined by dividing the power gearbox heat load by the fan power consumption function, the second quotient being determined by dividing the fan diameter by the bypass ratio of the turbofan engine.

The method of any preceding clause, wherein the heat exchanger capacity is between 6.17 and 48.0 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 6,000 m²/m³ and 13,000 m²/m³.

The method of any preceding clause, wherein the heat exchanger capacity is between 0.77 and 22.02 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 6,000 m²/m³.

A cooling system for a turbofan engine, comprising: one or more heat exchangers tied to a power gearbox mechanically coupling a fan with a spool of the turbofan engine, the one or more heat exchangers having a heat exchanger capacity defined by a resultant heat transfer surface area density associated with the one or more heat exchangers multiplied by a heat conductance factor that relates a power gearbox heat load of the one or more heat exchangers, a fan power consumption function associated with the fan, a fan diameter of the fan, and a bypass ratio of the turbofan engine, and wherein the heat exchanger capacity is between 0.77 and 48 for a rotational speed of the spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 13,000 m²/m³. 

We claim:
 1. A turbofan engine, comprising: a low pressure spool; a fan; a power gearbox mechanically coupling the low pressure spool and the fan; and one or more heat exchangers tied to the power gearbox, the one or more heat exchangers having a heat exchanger capacity defined by a resultant heat transfer surface area density associated with the one or more heat exchangers multiplied by a heat conductance factor that relates a power gearbox heat load, a fan power consumption function, a fan diameter of the fan, and a bypass ratio of the turbofan engine, and wherein the heat exchanger capacity is between 0.77 and 48 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 13,000 m²/m³.
 2. The turbofan engine of claim 1, wherein the resultant heat transfer surface area density is determined by taking a product to an Nth root, wherein the product is determined by multiplying together a heat transfer surface area density associated with each of the one or more heat exchangers tied to the power gearbox together, wherein N is a number of heat exchangers tied to the power gearbox.
 3. The turbofan engine of claim 2, wherein the one or more heat exchangers each have one or more exchanger units each having a core defining a plurality of channels.
 4. The turbofan engine of claim 3, wherein the heat transfer surface area density for a given one of the one or more heat exchangers is defined as a quotient determined by dividing a heat exchanger channel surface area associated with the plurality of channels of the given one of the one or more heat exchangers to a heat exchanger channel volume associated with the plurality of channels of the given one of the one or more heat exchangers.
 5. The turbofan engine of claim 1, wherein the heat conductance factor is defined as a product determined by multiplying a first quotient by a second quotient, the first quotient being determined by dividing the power gearbox heat load by the fan power consumption function, the second quotient being determined by dividing the fan diameter of the fan by the bypass ratio of the turbofan engine, wherein the power gearbox heat load is defined as a product determined by multiplying a maximum continuous thrust associated with the turbofan engine by one minus a power gearbox efficiency of the power gearbox and by a maximum continuous cruise speed associated with the turbofan engine, and wherein the fan power consumption function is defined as a product determined by multiplying a fan thrust function by a maximum cruise speed associated with the turbofan engine.
 6. The turbofan engine of claim 5, wherein the power gearbox efficiency is between 99.2 and 99.8.
 7. The turbofan engine of claim 5, wherein the fan thrust function is defined as a product determined by multiplying an air density of air at 11,000 m above sea level by a fan tip speed of the fan, squared, by a fan area of the fan, wherein the fan area is defined as a quotient determined by dividing a product by four, wherein the product is determined by multiplying pi by the fan diameter of the fan, squared, and wherein the fan tip speed of the fan is defined as a product determined by multiplying pi by the fan diameter of the fan by a quotient, the quotient being determined by dividing a rotational speed of the low pressure spool by a gear ratio of the power gearbox.
 8. The turbofan engine of claim 1, wherein the heat exchanger capacity is between 6.17 and 48.0 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 6,000 m²/m³ and 13,000 m²/m³.
 9. The turbofan engine of claim 1, wherein the heat exchanger capacity is between 0.77 and 22.02 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 6,000 m²/m³.
 10. The turbofan engine of claim 1, wherein the heat exchanger capacity is between 8.23 and 48.0 for a rotational speed of the low pressure spool between 2,000 and 10,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 6,000 m²/m³ and 13,000 m²/m³.
 11. The turbofan engine of claim 1, wherein the heat exchanger capacity is between 6.17 and 17.84 for a rotational speed of the low pressure spool between 10,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 6,000 m²/m³ and 13,000 m²/m³.
 12. The turbofan engine of claim 1, wherein the heat exchanger capacity is between 1.03 and 22.02 for a rotational speed of the low pressure spool between 2,000 and 10,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 6,000 m²/m³.
 13. The turbofan engine of claim 1, wherein the heat exchanger capacity is between 0.77 and 8.23 for a rotational speed of the low pressure spool between 10,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 6,000 m²/m³.
 14. The turbofan engine of claim 1, wherein the one or more heat exchangers include a fuel-to-oil heat exchanger, an air-to-oil heat exchanger, and an oil-to-oil heat exchanger.
 15. The turbofan engine of claim 1, wherein the one or more heat exchangers include at least four heat exchangers.
 16. A method, comprising: operating a turbofan engine having a low pressure spool, a fan, a power gearbox mechanically coupling the low pressure spool and the fan, and one or more heat exchangers tied to the power gearbox, and wherein the one or more heat exchangers have a heat exchanger capacity defined by a resultant heat transfer surface area density associated with the one or more heat exchangers multiplied by a heat conductance factor that relates a power gearbox heat load associated with the one or more heat exchangers, a fan power consumption function of the fan, a fan diameter of the fan, and a bypass ratio of the turbofan engine, and wherein the heat exchanger capacity is between 0.77 and 48 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 13,000 m²/m³.
 17. The method of claim 16, wherein the resultant heat transfer surface area density is determined by taking a product to an Nth root, wherein the product is determined by multiplying a heat transfer surface area density associated with each of the one or more heat exchangers tied to the power gearbox together, wherein N is a number of heat exchangers tied to the power gearbox, the heat transfer surface area density for a given one of the one or more heat exchangers is defined as a quotient determined by dividing a heat exchanger channel surface area associated with a plurality of channels of the given one of the one or more heat exchangers to a heat exchanger channel volume associated with the plurality of channels of the given one of the one or more heat exchangers, and wherein the heat conductance factor is defined as a product determined by multiplying a first quotient by a second quotient, the first quotient being determined by dividing the power gearbox heat load by the fan power consumption function, the second quotient being determined by dividing the fan diameter by the bypass ratio of the turbofan engine.
 18. The method of claim 16, wherein the heat exchanger capacity is between 6.17 and 48.0 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 6,000 m²/m³ and 13,000 m²/m³.
 19. The method of claim 16, wherein the heat exchanger capacity is between 0.77 and 22.02 for a rotational speed of the low pressure spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 6,000 m²/m³.
 20. A cooling system for a turbofan engine, comprising: one or more heat exchangers tied to a power gearbox mechanically coupling a fan with a spool of the turbofan engine, the one or more heat exchangers having a heat exchanger capacity defined by a resultant heat transfer surface area density associated with the one or more heat exchangers multiplied by a heat conductance factor that relates a power gearbox heat load of the one or more heat exchangers, a fan power consumption function associated with the fan, a fan diameter of the fan, and a bypass ratio of the turbofan engine, and wherein the heat exchanger capacity is between 0.77 and 48 for a rotational speed of the spool between 2,000 and 16,000 revolutions per minute at one hundred percent capacity and a resultant heat transfer surface area density being between 3,000 m²/m³ and 13,000 m²/m³. 